Further delays on a $34 million project to co-locate Benjamin Franklin High School and Science Leadership Academy inside the same building on North Broad Street mean 1,000 students from the two schools won’t be going back to classes Thursday as planned, officials have confirmed.

Students now are scheduled to return on Friday; in an email to parents, Shawn Bird, the Philadelphia School District’s chief of schools, said the decision was made “in an abundance of caution.”

Officials said Ben Franklin and SLA students would not have to make up days missed due to construction delays.

It’s the second time the start of school has been pushed back for Ben Franklin, a neighborhood high school, and SLA, a nationally renowned magnet school.

Students at every other school in the district began classes Tuesday, but officials made the call last week to delay the start for SLA and Ben Franklin because the six-story building’s elevators were not yet operational.

Sources with firsthand knowledge of the building conditions said much work remains to be done.

“It’s a mess,” said one source, who was not authorized to speak on the record about the building conditions. “There’s wires everywhere. There’s heating units that are not covered and water in the floor in some places.”

Staff have concerns about air quality, the source said.

“This is an active construction site,” said the source. “People have asthma concerns. People have worries about the students being in the building.”

A letter to superintendent William R. Hite Jr., the school board, union officials and others, obtained by The Inquirer and signed by “the staff of Benjamin Franklin High School and Science Leadership Academy — Center City" said “this building is not safe, not functional, and certainly not ready to admit students tomorrow.”

The teachers wrote that several restrooms, all science labs, the gym and the kitchen facilities were not functional as of Wednesday.

“The elevators are either not functioning or not available for use,” the teachers wrote.

As a result of the problems, multiple classes will have to share rooms, science and gym teachers will have to rewrite early lesson plans, and the kitchen staff will have to order meals from offsite.

Bird said in the email to parents that the passenger elevator, which will be used to transport students with physical disabilities, still must be inspected, and that a cleaning crew would be on site Thursday. Officials blamed the first delay on nonoperational elevators.

“Our top priority remains to provide a healthy, safe, and welcoming learning environment for students and staff,” Bird wrote.

Asbestos abatement has been finished, Bird said, and the work areas have been tested and passed inspection. Those reports will be available publicly.

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The teachers said they did not take any cancellation of student learning time lightly, “but we cannot remain silent while our students are at risk. The fact that Benjamin Franklin students and staff are facing these conditions for a second year is not proof that they are acceptable; it is all the more reason why they should not have to go through more of the same!"

Although students are now scheduled to return Friday, not all construction work will be complete. Some areas of the building will be closed off to students and staff at first.

When complete, the building is expected to be impressive; a committee of Ben Franklin and SLA students and staff gave input into its design, two years in the making.

SLA had been housed in rented space in Center City that was costing the district $1.5 million annually; Ben Franklin is a 242,293-square-foot building in Spring Garden that can house more than 1,500 students, but last year had just 425. Across the city and in urban districts around the country, the school choice movement has emptied out many comprehensive high schools.

Once open, the schools will maintain separate entrances: Ben Franklin students will enter on Broad, and SLA students temporarily on North 15th Street, but eventually on Green Street. Students will not share classes or a lunchroom, although officials said they would find ways to give the young people opportunities to congregate.